Device for detecting gases for use in diffusion and forced flow modes

Abstract

A gas detection device is provided comprising an exterior housing in which an active pelement and a compensating pelement are disposed. The gas detection device further comprises a porous frit seated within a distal end of the exterior housing to separate the active pelement and the compensating pelement from the surrounding environment. The porous frit is adapted to prevent flashback into the surrounding environment while allowing movement of environmental gas through the porous frit to contact the active pelement and the compensating pelement. The gas detection device further comprises a flow guide for directing flow of environmental gas into the gas detection device disposed adjacent the exterior side of the porous frit. The flow guide comprises an inlet port through which a forced flow of environmental gas is pumped to pass through the porous frit and into the exterior housing in a direction generally parallel to the axis of the exterior housing. The flow guide also comprises an outlet port through which gas may exit the exterior housing. A gas detection device is also provided in which the electrical resistance of the compensating pelement is measured to determine concentration of combustible gas at combustible gas concentration levels above a predetermined concentration level set equal to the LEL (Lower Explosive Limit). The gas detection comprises a circuit for reducing current passing through the active pelement when the gas detection device is being used above the predetermined concentration level.

What is claimed is: 
     
       1. A gas detection device for the detection of combustible gases in a surrounding environment comprising, an exterior housing, an active pelement disposed within the exterior housing and a compensating pelement disposed within the exterior housing, the gas detection device further comprising a porous frit seated within a distal end of the exterior housing to separate the active pelement and the compensating pelement from the surrounding environment, the porous frit adapted to prevent flashback into the surrounding environment while allowing entry of environmental gas through the porous frit to contact the active pelement and the compensating pelement, the porous frit having an interior side within the exterior housing and an exterior side outside the exterior housing, the gas detection device further comprising a flow guide for directing flow of environmental gas into the gas detection device disposed adjacent the exterior side of the porous frit, the flow guide comprising an inlet port through which a forced flow of environmental gas is directed by an external pump to pass through the porous frit and into the exterior housing in a direction generally parallel to the axis of the exterior housing to contact the active pelement and the compensating pelement, the flow guide further comprising an outlet port through which gas may exit the exterior housing. 
     
     
       2. The gas detection device of claim 1 wherein the flow guide further comprises a bypass passage for allowing a portion of environmental gas pumped to the inlet port to bypass the porous frit in a flow controlling function that never permits said portion of environmental gas to enter within the exterior housing. 
     
     
       3. The gas detection device of claim 2 wherein the bypass passage comprises a channel providing fluid connection between the inlet port and the outlet port. 
     
     
       4. The gas detection device of claim 2 further comprising an interior housing, the interior housing comprising a first filament well therein in which the compensating pelement is disposed and a second filament well therein in which the active pelement is disposed, the interior housing further comprising a passage for providing fluid connection between the first filament well and the second filament well. 
     
     
       5. The gas detection device of claim 2 further comprising an interior housing, the interior housing comprising a first filament well therein in which the compensating pelement is disposed and a second filament well therein in which the active pelement is disposed, the gas detection device further comprising a porous membrane disposed adjacent the interior housing, the gas detection device further comprising a flow director disposed adjacent the porous membrane, the flow director comprising a first passage therethrough, the first passage being in generally linear alignment with the first well to provide substantially direct fluid contact with the first well through the porous film, the flow director also comprising a second passage therethrough, the second passage being in generally linear alignment with the second well to provide substantially direct fluid contact with the second well through the porous film, the flow director further comprising a passage therein for providing fluid connection between the first passage and the second passage, the inlet port being in generally linear alignment with the first passage in the flow director to provide substantially direct fluid connection between the inlet port and the first passage through the porous frit, the outlet port being in generally linear alignment with the second passage in the flow director to provide substantially direct fluid connection between the outlet port and the second passage in the flow director through the porous frit. 
     
     
       6. The gas detection device of claim 5 wherein the porous film is fabricated of a polytetrafluoroethylene material. 
     
     
       7. The gas detection device of claim 6 further comprising a filter to remove certain contaminants from environmental gas flowing therethrough to prevent detrimental effects of such contaminants. 
     
     
       8. The gas detection device of claim 1 wherein the electrical resistance of the compensating pelement is used to determine concentration of combustible gas above a predetermined combustible gas concentration level. 
     
     
       9. The gas detection device of claim 8 further comprising a circuit for reducing current passing through the active pelement, thereby reducing the temperature of the active pelement below a temperature at which substantial catalytic oxidation occurs, when the gas detection device is being used in an environment where the level of combustible gas is above the predetermined concentration level of combustible gas. 
     
     
       10. The gas detection device of claim 9 wherein the circuit for reducing current passing through the active pelement comprises a transistor in parallel electrical connection with the active pelement, the transistor adapted to be switchable between a high-conductivity state and a low-conductivity state. 
     
     
       11. A gas detection device comprising an active pelement, a compensating pelement and a circuit for measuring the electrical resistance of the compensating pelement, wherein the electrical resistance of the compensating pelement is used to determine concentration of combustible gas at combustible gas concentration levels above a 100% LEL (Lower Explosive Limit). 
     
     
       12. The gas detection device of claim 11 further comprising a circuit for reducing current passing through the active pelement, thereby reducing the temperature of the active pelement below a temperature at which substantial catalytic oxidation occurs, when the gas detection device is being used above the predetermined concentration level. 
     
     
       13. The gas detection device of claim 12 wherein the circuit for reducing current passing through the active pelement comprises a transistor in parallel electrical connection with the active pelement, the transistor adapted to be switchable between a high-conductivity state and a low-conductivity state.